1. Field of the Invention
This invention relates to improved lithography systems and methods. More specifically, this invention relates to microlithography systems and methods having a high numerical aperture.
2. Background Art
Lithography is a process used to create features on the surface of substrates. Such substrates can include those used in the manufacture of flat panel displays, circuit boards, various integrated circuits, and the like. A frequently used substrate for such applications is a semiconductor wafer. While this description is written in terms of a semiconductor wafer for illustrative purposes, one skilled in the art would recognize that this description also applies to other types of substrates known to those skilled in the art. During lithography, a wafer, which is disposed on a wafer stage, is exposed to an image projected onto the surface of the wafer by exposure optics located within a lithography apparatus. The image refers to the original, or source, image being exposed. The projected image refers to the image incident on the surface of the wafer. While exposure optics are used in the case of lithography, a different type of exposure apparatus may be used depending on the particular application. For example, some lithographies each may require a different exposure apparatus, as is known to those skilled in the art. The particular example of lithography is discussed here for illustrative purposes only.
The projected image produces changes in the characteristics of a layer, such as photoresist, deposited on the surface of the wafer. These changes correspond to the features projected onto the wafer during exposure. Subsequent to exposure, the layer can be etched to produce a patterned layer. The pattern corresponds to those features projected onto the wafer during exposure. This patterned layer is then used to remove exposed portions of underlying structural layers within the wafer, such as conductive, semiconductive, or insulative layers. This process is then repeated, together with other steps, until the desired features have been formed on the surface of the wafer.
Step-and-scan technology works in conjunction with a projection optics system that has a narrow imaging slot. Rather than expose the entire wafer at one time, individual fields are scanned onto the wafer one at a time. This is done by moving the wafer and reticle such that the imaging slot is moved across the field during the scan. The wafer stage must then be stepped between field exposures to allow multiple copies of the reticle pattern to be exposed over the wafer surface. In this manner, the quality of the image projected onto the wafer is maximized.
The following patents describe examples of conventional technology for generating images on the semiconductor wafer from a pattern on the reticle: U.S. Pat. No. 4,953, 960, to Williamson, U.S. Pat. No. 5,212,593, to Williamson et al., U.S. Pat. No. 5,537,260, to Williamson, U.S. Pat. No. 5,636,066, to Takahashi, U.S. Pat. No. 5,583,696, to Takahashi, U.S. Pat. No. 5,691,802, to Takahashi, U.S. Pat. No. 5,808,805, to Takahashi, U.S. Pat. No. 5,835,284, to Takahashi, U.S. Pat. No. 5,969,882, to Takahashi.